An Ocean Thermal Energy Conversion (OTEC) system generates electrical energy based on a temperature difference between cold seawater deep in the ocean and warm seawater near the ocean surface. Typically, OTEC systems rely upon large, robust heat exchangers that transfer heat between a working fluid and the seawater as part of a Rankine-cycle engine.
In the Rankine cycle, the working fluid is vaporized by absorption of heat from the warm seawater at one or more heat exchangers, configured as evaporators. The vaporized working fluid passes through a turbogenerator to induce it to generate electrical energy. After the vaporized working fluid has passed through the turbogenerator, it is condensed back into liquid form at one or more heat exchangers, configured as condensers. At these condensers, heat from the working fluid is absorbed by cold seawater pumped into the condensers from a depth of 1000 meters or more. The liquefied working fluid is then pumped back to the evaporators to be vaporized again, thus continuing the Rankine cycle.
The evaporators and condensers are sometimes located on a ship or on the deck of an offshore platform, such as platforms used in offshore oil drilling, etc. It is preferable, however, that they are submerged below the water line to reduce platform costs and preserve deck space, among other reasons. In some cases, evaporators or condensers are housed in submerged compartments that are part of the offshore platform itself.
The heat exchangers and pumping systems that feed seawater to them represent some of the largest capital and operational costs of an OTEC installation. As a result, it is highly desirable, if not necessary, that the seawater delivery and pumping systems are cost-effective, minimize parasitic losses, and enable the flow of large volumes of seawater through the heat exchangers.